Heretofore, upon a lighting equipment and so on, there has been used that a plurality of serially connected LED circuits, in which many LED devices are serially connected, is connected in parallel, and an electrical current flowing through the plurality of serially connected LED circuits is turned on and off by using a switching device (transistor) so as to control turning on and off the many LED devices with all together (see, for example, Japanese laid-open patent publication No. 2001-15278, No. 2003-100472, No. 2003-139712, No. 2005-50704).
FIG. 1 is a view showing a conventional general structure of such an LED driving circuit. A serially connected LED circuit 11 is formed by connecting many LED devices in series, and DC power supply 12 and a switching device 13 are connected in series with the serially connected LED circuit 11. A control circuit 14 is connected to a control terminal (base terminal) of the switching device (transistor) 13 and a control signal is supplied for turning on and off the switching device 13. When an on-signal voltage is supplied to the switching device 13, the switching device 13 between a collector and an emitter becomes on-state, and an electrical current is supplied from DC power supply 12 to flow through the many LED devices to turning on with all together. When an off-signal voltage is supplied to the switching device 13, the switching device 13 between the collector and the emitter becomes off-state, and the electrical current from the power supply 12 is shut off to turning off the many LED devices with all together.